Cytomegalovirus (CMV) is a ubiquitous virus that commonly infects people across the spectrum of all ages, races, and ethnic groups, and those from a variety of socioeconomic, cultural, and geographic backgrounds. Although most CMV infections are asymptomatic or cause mild disease, the virus can cause serious disease in newborns and immunocompromised children . Discerning which role, if any, CMV is playing in a disease process, as well as the need for treatment, can be difficult because of its ubiquity. Such decisions require a thorough knowledge of CMV virology, epidemiology, clinical manifestations, laboratory diagnosis, and indications for treatment.
Cytomegalovirus (CMV) is a member of the Herpesvirus family, along with Epstein-Barr virus (EBV); herpes simplex viruses (HSV)-1 and 2; varicella-zoster virus (VZV); and human herpesviruses (HHV)-6, -7, and -8. These viruses all share properties, including a genome of double-stranded linear DNA, a virus capsid of icosahedral symmetry, and a viral envelope . They also share the biological properties of latency and reactivation, which cause recurrent infections in the host.
CMV is a member of the subfamily beta Herpesviridae, which also contains HHV-6 and -7. CMV will replicate slowly, often taking as long as 24 hours to produce virus progeny in infected cells and several days to weeks to produce visible cytopathic effect in laboratory cell lines (picture 1). No distinct serotypes of CMV exist; however, strain differences can be detected by molecular analysis of DNA, providing a classification of genotypes .
EPIDEMIOLOGY AND TRANSMISSION
Infection with cytomegalovirus (CMV) occurs commonly; seroepidemiologic studies have shown the prevalence of antibody to CMV is influenced by age, geography, cultural and socioeconomic status, and child-rearing practices. In developing countries, most children are infected by three years of age, whereas in developed countries, such as the United States or United Kingdom, as many as 60 to 80 percent of the population will be infected with CMV by adulthood .
Congenital infection — Approximately 1 percent (0.2 to 2.5 percent) of newborns are born congenitally infected with CMV. Most of these newborns appear normal and are asymptomatic, but 5 to 15 percent of congenitally infected newborns will have symptoms at birth . Both maternal primary and recurrent infection during pregnancy can result in congenital infection of the infant, but the rate of transmission is far higher for mothers with primary infection (40 versus <1 percent transmission). Infants born congenitally infected with CMV as a result of a primary maternal infection also are much more likely to have symptoms at birth and suffer sequelae than newborns born congenitally infected from a maternal recurrent CMV infection. Newborns with a primary immune disorder of cellular function (eg, severe combined immune deficiency or natural killer (NK) cell disorders) may also manifest severe or fatal congenital CMV infection. (See "Severe combined immunodeficiency (SCID): An overview" and "NK cell deficiency syndromes: Clinical manifestations and diagnosis", section on 'Clinical and laboratory features'.)